The present invention relates to a method of manufacturing a magnetic recording medium and, more particularly, to a method of manufacturing a magnetic recording medium in which the step of dispersing a magnetic powder in a binder is improved.
A magnetic recording medium is conventionally manufactured by the following method. First, a needle-like .gamma.-ferrite powder or a Co-coated .gamma.-ferrite powder is dissolved in a solvent or mixed with a binder resin to prepare a magnetic paint. The magnetic paint is then applied on the surface of a base material such as a polyester film and dried to prepare a magnetic recording medium.
Demand for high-density in magnetic recording media is strong. In order to satisfy this, various methods have been proposed including a method of reducing the size of .gamma.-ferrite particles and a method of using a reducing powder (metal powder). The most important factor in the manufacture of a high-density magnetic recording medium is the dispersion of such an ultrafine powder in a binder resin. In view of this, great effort has been made to achieve satisfactory dispersion. Various techniques have been proposed including an improvement in the surface properties of a magnetic powder, various dispersion mixers, and dispersion processes, and new dispersants or binder resins. Among these dispersion techniques, the wet dispersion method has been generally adopted. According to this method, a magnetic powder together with a dispersant or a binder resin is dispersed in water or in an organic solvent by a dispersion mixer such as a dissolver, a kneader, a ball mill, a sand grinder, or a paint shaker. This method is generally adopted because magnetic powders such as needle-like .gamma.-ferrite powders or metal powders are less resistant to mechanical stress and crack easily. Also, metal powders are easily oxidized and, when dry, may catch fire or explode. Such powders must be treated in a wet state. Conventional magnetic powder dispersion methods require complex and cumbersome procedures and means, resulting in low productivity.